Psst. The Recession Is Over.

As the old joke goes, economists are so sharp they have predicted eight of the last five recessions. The real problem, however, may be that they are too slow to call recoveries.

Employment, which usually lags the recovery, surged in February, and positive developments are so widespread that the beleaguered industrial sector posted solid growth this year. Even dour Alan Greenspan is making chirpy noises. But the National Bureau of Economic Research, an independent agency that over the years acquired the role of...